The present invention relates to a motor driving device and a motor driving method capable of applying a short brake and a reverse brake to a motor.
A motor can be stopped by decelerating the motor with a short brake or with a reverse brake. A conventional motor driving device has a short brake mode in which a short brake is applied to the motor and a reverse brake mode in which a reverse brake is applied to the motor, one of which is selected for deceleration and stopping of the motor.
In the short brake mode, the motor is decelerated by forming a short circuit between the terminals of motor windings of three phases. In the reverse brake mode, the motor is decelerated by applying a reverse current through motor windings of a plurality of phases to excite the motor windings in the reverse direction.
FIG. 9 is a diagram illustrating a configuration of a conventional motor driving device 1E.
Referring to FIG. 9, the motor driving device 1E includes position detection means 10, energization switching signal production means 20, rotation control means 30, brake command generation means 40, brake mode switching means 50D, reverse rotation detection means 60, energization control signal production means 70D, and power transistors Q1 to Q6. A motor M1 provided outside the motor driving device 1E includes a rotor r1, and motor windings L1 to L3 for rotating a disk d1 via the rotor r1.
The operation of the conventional motor driving device 1E will now be described below in detail.
FIG. 10 is a diagram illustrating an internal configuration of the brake mode switching means 50D illustrated in FIG. 9.
During normal rotation of the motor M1, torque command generation means 41 provided in the brake command generation means 40 outputs a torque command signal S2 based on a rotation control signal S1 from the rotation control means 30. The energization switching signal production means 20 receives the torque command signal S2 and outputs, to the energization control signal production means 70D, an energization switching signal S4 having a level according to that of the torque command signal S2 for energizing the motor windings of a plurality of phases with an energization angle that is determined based on a position signal S3 from the position detection means 10. The energization control signal production means 70D successively energizes the power transistors Q1 to Q6 based on the energization switching signal S4. The rotation control means 30 may be a microcomputer, for example. As the position signal S3 is received from the position detection means 10, the microcomputer counts the number of cycles of the received position signal S3 to obtain count data, and compares the obtained count data with reference data stored therein that corresponds to the number of revolutions per unit time, so as to output the rotation control signal S1 according to the comparison result. The torque command generation means 41, which may be a smoothing circuit, outputs a DC voltage, which is obtained by smoothing the rotation control signal S1, as the torque command signal S2.
The brake command generation means 40 outputs a brake command signal S5 based on the rotation control signal S1 from the rotation control means 30. Then, the brake mode switching means 50D, which includes logic circuits 511d and 512d as illustrated in FIG. 10, receives the brake command signal S5 and a brake mode switching signal S111, and selects one of the short brake mode and the reverse brake mode.
In a case where the short brake mode is selected, the brake mode switching means 50D selectively outputs a short brake signal /S7 based on the brake mode switching signal S11. The energization control signal production means 70D receives the energization switching signal S4 from the energization switching signal production means 20 and the short brake signal /S7 to output an energization control signal S8 to the power transistors Q1 to Q6. Based on the energization control signal S8, the power transistors Q1, Q3 and Q5 may be all turned ON, with the power transistors Q2, Q4 and Q6 being all turned OFF. Alternatively, the power transistors Q2, Q4 and Q6 may be all turned ON, with the power transistors Q1, Q3 and Q5 being all turned OFF, to form a short circuit between the terminals of the motor windings L1, L2 and L3 of three phases so that a counter electromotive voltage is consumed in the motor windings L1, L2 and L3, thereby decelerating and stopping the motor M1.
In a case where the reverse brake mode is selected, the brake mode switching means 50D selectively outputs a reverse brake signal S7 based on the brake mode switching signal S11. The energization control signal production means 70D receives the energization switching signal S4 from the energization switching signal production means 20 and the reverse brake signal S7 to output the energization control signal S8 of the reverse polarity to the power transistors Q1 to Q6. The power transistors Q1 to Q6 apply the energization control signal S8 of the reverse polarity to the motor windings L1, L2 and L3 of the three phases so as to excite the motor windings L1, L2 and L3 in the reverse direction, thereby braking the rotor r1.
In such a case, the reverse rotation detection means 60 detects a reverse rotation by, for example, detecting the cycle of the output signal from the position detection means 10 using a timer, or the like. Specifically, the reverse rotation detection means 60 determines that the motor is standing when detecting that the cycle of the position signal S3 from the position detection means 10 is equal to or greater than a predetermined value, and outputs a reverse rotation signal S9 assuming that the motor is about to start rotating in the reverse direction. When receiving the reverse rotation signal S9, the energization control signal production means 70D stops supplying the energization control signal S8 to all the motor windings L1, L2 and L3. Then, the motor M1 comes to a complete stop after continuing to rotate with the force of inertia.
As described above, the conventional motor driving device brakes the motor M1 by selecting either one of the short brake mode and the reverse brake mode. The short brake mode is advantageous in that the motor M1 makes substantially no braking noise, and is effective during high-speed rotation because the braking force in this mode is dependent on the counter electromotive voltage. However, the braking force decreases as the number of revolutions decreases, thereby taking a long time for the motor to come to a complete stop.
On the other hand, the reverse brake mode provides a large braking force because the motor windings L1 to L3 are excited in the reverse direction while decelerating the motor. However, during high-speed rotation, the motor makes substantial noise due to a phase shift. Moreover, it is difficult to detect a reverse rotation with a high precision, and if the control fails to stop the energization control signal S8 of the reverse polarity at an appropriate timing, the reverse excitation continues for a while even after the motor M1 stops, whereby the motor M1 starts rotating in the reverse direction. Although the energization control signal production means 70D thereafter stops energizing the motor windings L1 to L3 of the three phases, the motor M1 will continue to rotate for a while with the force of inertia. Therefore, it takes a long time for the motor to come to a complete stop, and causes an error in the position at which the motor M1 stops.
It is an object of the present invention to provide a motor driving device and a motor driving method capable of stopping a motor while reducing the braking noise and the stopping time.
Specifically, a motor driving device of the present invention includes: brake mode switching signal production means for detecting the number of revolutions per unit time of a rotor according to a change in a positional relationship between motor windings of a plurality of phases and the rotor so as to output a brake mode switching signal for selecting either a short brake mode or a reverse brake mode for braking the rotor based on the number of revolutions; and control means for outputting an energization control signal for controlling energization of the motor windings of a plurality of phases in response to the brake mode switching signal.
In this way, it is possible to switch brake modes from one to another according to the number of revolutions of the motor. Therefore, it is possible to reduce the braking noise and the stopping time. Moreover, it is less likely that an error occurs in the position at which the motor stops.
Another motor driving device of the present invention includes: position detection means for outputting a position signal representing a positional relationship between motor windings of a plurality of phases and a rotor; rotation detection means for outputting a detection signal according to a number of revolutions per unit time of the rotor; rotation control means for outputting a rotation control signal for controlling rotation of the rotor; brake command generation means for outputting a torque command signal according to the rotation control signal upon receiving the rotation control signal and for outputting a brake command signal for applying a short brake or a reverse brake to the rotation of the rotor; energization switching signal production means for outputting an energization switching signal having a level according to that of the torque command signal for energizing the motor windings of a plurality of phases with an energization angle that is determined based on the position signal; rotation determination means for comparing the number of revolutions per unit time detected by the rotation detection means with a predetermined number of revolutions, by using signals that are equivalent to the numbers of revolutions, to output a brake mode switching signal for selecting either the short brake or the reverse brake; brake mode switching means for selecting either one of the brake modes based on the brake command signal and the brake mode switching signal and outputting a brake mode command signal indicating selected brake mode; energization control signal production means for outputting an energization control signal for controlling energization of the motor windings of a plurality of phases based on the brake command signal, the brake mode command signal and the energization switching signal; and a plurality of transistors for supplying a power to the motor windings of a plurality of phases according to the energization control signal.
In this way, it is possible to switch brake modes from one to another according to the number of revolutions of the motor. Therefore, it is possible to reduce the braking noise and the stopping time. Moreover, it is less likely that an error occurs in the position at which the motor stops. Furthermore, since the predetermined number of revolutions to be the switching reference can be set arbitrarily, it is possible to control the amount of time required for the motor to come to a complete stop.
It is preferred that the motor driving device further includes clock signal production means for producing a clock signal having a predetermined frequency and a predetermined duty ratio, wherein the brake mode switching means further receives the clock signal to output the brake mode command signal based also on the clock signal.
It is preferred that the motor driving device further includes: current value detection means for detecting a value of a current flowing through the motor windings of a plurality of phases; and current value determination means for comparing a detection signal from the current value detection means with a predetermined reference value to output, to the brake mode switching means, a current value determination signal whose signal level transitions according to the comparison result, wherein the brake mode switching means outputs the brake mode command signal at a timing that is determined according to the current value determination signal.
It is preferred that the motor driving device further includes OFF signal production means for outputting an OFF signal, which is a pulse having a predetermined cycle, when receiving the brake mode switching signal, wherein when receiving the OFF signal output from the OFF signal production means, the energization control signal production means outputs an energization control signal to the plurality of transistors for temporarily stopping a current supply to the motor windings of a plurality of phases according to the OFF signal.
A motor driving method of the present invention includes: motor windings of a plurality of phases; a rotor; a plurality of transistors for driving the motor windings of a plurality of phases; and a control circuit for detecting a number of revolutions per unit time of the rotor according to a change in a positional relationship between the motor windings of a plurality of phases and the rotor so as to control a braking operation of the plurality of transistors, wherein the control circuit performs a short brake control of shorting terminals of the motor windings of a plurality of phases with one another while a rotational speed of the rotor is a first rotational speed, a reverse brake control of applying a reverse driving current to the motor windings of a plurality of phases while the rotational speed of the rotor is a second rotational speed that is lower than the first rotational speed, and then the short brake control again while the rotational speed of the rotor is a third rotational speed that is lower than the second rotational speed.
Thus, while the number of revolutions is the first number of revolutions, the short brake control is used, thereby reducing noise that is generated when decelerating the motor from a high-speed rotation. While the number of revolutions is the second number of revolutions, the reverse brake control is used, thereby quickly decreasing the rotational speed of the motor. While the number of revolutions is the third number of revolutions, the short brake control is used again, whereby the motor can be brought to a complete stop within a short period of time, and it is possible to stop the motor at an accurate position without having to detect a reverse rotation as is necessary in the prior art.
Another motor driving method of the present invention includes: motor windings of a plurality of phases; a rotor; a plurality of transistors for driving the motor windings of a plurality of phases; and a control circuit for detecting a number of revolutions per unit time of the rotor according to a change in a positional relationship between the motor windings of a plurality of phases and the rotor so as to control a braking operation of the plurality of transistors, wherein the control circuit performs a short brake control of shorting terminals of the motor windings of a plurality of phases with one another while a rotational speed of the rotor is a first rotational speed, a mixed brake control in which the short brake control and a reverse brake control of applying a reverse driving current to the motor windings of a plurality of phases are repeatedly switched from one to another based on a clock signal having a predetermined cycle and a predetermined duty ratio while the rotational speed of the rotor is a second rotational speed that is lower than the first rotational speed, and then the short brake control again while the rotational speed of the rotor is a third rotational speed that is lower than the second rotational speed.
Thus, while the number of revolutions is the second number of revolutions, the mixed brake control in which the short brake control and the reverse brake control are repeatedly switched from one to another is performed, thereby realizing a smooth transition from the short brake control for the first number of revolutions to the next brake control for the second number of revolutions. Thus, it is possible to reduce noise that may otherwise occur at the brake mode transition.
It is preferred that a one-shot pulse is generated when switching the short brake control and the reverse brake control from one to another for turning OFF all of the plurality of transistors according to the one-shot pulse.